By Cassie Werber 

LONDON--Crude oil futures headed down Friday as a selloff continued, sending U.S. contract to its lowest point since early February, as seasonal lows also took effect.

Summer is a time of lower demand from refineries as they carry out maintenance, according to analysts at JBC Energy. Profit margins for products are also low at the moment, leading to reduced refinery intakes, they said.

Moreover, there are plenty of oil stocks in the system.

"The oil market looks fairly oversupplied following the ample crude stocks in Europe and the U.S.," said Myrto Sokou, senior research analyst at Sucden Research.

In July, Brent futures had their worst monthly performance since April 2013, falling more than $6 during the month, she said. Brent September crude on ICE was down 0.6% at $105.42 a barrel.

WTI crude on the Nymex exchange was down 0.89% at $97.28 a barrel, its lowest since Feb. 7. Nymex WTI lost $2.10 a barrel during yesterday's trading with the intraday price hitting its lowest level since mid-March.

Investors are broadly brushing off the geopolitical concerns that continue to wash around the world. Oil's reaction to sanctions imposed on Russia this week by the European Union and U.S. was muted, with investors waiting to see how the news will affect the global economy more generally.

Despite stronger data from the U.S. on Thursday, some analysts believe the Russian concerns may come back to haunt oil investors.

"Russia sanctions may be the tipping point for the euro-zone economy sending it into deflation but it may also be the final straw that breaks the camel's back of confidence for U.S. stock market investors," said David Hufton of PVM.

Nonfarm payroll data, a marker of how well the U.S. economy is doing in terms of job creation, are due later Friday.

Recently the ICE's gas oil contract for August delivery was down $1.75 at $885.25 a metric ton, while Nymex gasoline for September delivery was down 158 points at $2.7814 a gallon.

Write to Cassie Werber at cassie.werber@wsj.com

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